/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicMesh3.h
Insert triangle at given index, assuming it is unused. If bUnsafe, we use fast id allocation that does not update free list. You should only be using this betweenBeginUnsafeTrianglesInsert()/EndUnsafeTrianglesInsert()calls
[EMeshResult](API\Runtime\GeometryCore\UE__Geometry__EMeshResult) InsertTriangle ( int TriangleID, const [FIndex3i](API\Runtime\GeometryCore\FIndex3i) & TriVertices, int GroupID, bool bUnsafe )